1. Field of the Invention
The invention relates to a piston/cylinder unit comprising a working cylinder, a piston attached to a piston rod and arranged in the working cylinder so that it is axially displaceable in the working cylinder, and a fastening element screwed into a threaded bore of the piston rod.
2. Description of the Related Art
Prior art piston/cylinder units, e.g. self-pumping hydropneumatic spring struts with internal leveling, are disclosed, for example, in German reference DE 33 16 069A1 in which a tubular piston rod is closed at its outer end by a screw-in bolt. The screw-in bolt has an offset which is pressed onto the end of the piston rod by the torque applied to the threaded joint. This type of piston-rod closure offers the advantage of allowing different screw-in bolts to be threaded into the piston rod so that the same piston rod can be used with many different screw-in bolts. This threaded joint is designed principally for transmitting forces in the axial direction, that is to say for elements constructed as axle dampers (shock absorbers).
The disadvantage with these embodiments is that, when these piston/cylinder units are used in spring struts, the screw-in bolts of the piston rod are exposed to bending loads at different wheel locations. Therefore, the screw-in bolts must accept the bending loads. The bending strength of a spring strut of this kind is dependent on the contact pressure on the end of the piston rod, said contact pressure being generated by the torque. Tests in the field have shown that, because the contact-pressure surface is at right angles to the center line, the threaded joint either loosens or, the screw-in bolt may shear off at this point.